From: Dominik Bathon <dbatml@...>
Date: 2005-05-30T22:33:41+09:00
Subject: Re: Tiling Turmoil (#33)

On Mon, 30 May 2005 13:30:21 +0200, atgeirr <atgeirr@math.uio.no> wrote:

> As far as I can understand, dup would actually work here, since the
> Array contains only numbers. Is that correct? Anyway, I did not know
> about dup, so thanks! I do not really understand the difference between
> dup and clone, though.

#clone works like #dup, but it keeps more properties of the original  
object:

#clone keeps a frozen object frozen, while #dup doesn't:

irb(main):007:0> a="hallo"
=> "hallo"
irb(main):008:0> a.freeze
=> "hallo"
irb(main):009:0> a.frozen?
=> true
irb(main):010:0> a.dup.frozen?
=> false
irb(main):011:0> a.clone.frozen?
=> true

and a cloned singleton class can not be instantieted, while a dupped  
singleton class can:

irb(main):012:0> (class << a; self; end).new
TypeError: can't create instance of virtual class
         from (irb):12:in `new'
         from (irb):12
         from :0
irb(main):013:0> (class << a; self; end).clone.new
TypeError: can't create instance of virtual class
         from (irb):13:in `new'
         from (irb):13
         from :0
irb(main):014:0> (class << a; self; end).dup.new
=> ""

For the full details, here is the source of both functions from  
ruby-1.8.2/object.c:

VALUE
rb_obj_clone(obj)
     VALUE obj;
{
     VALUE clone;

     if (rb_special_const_p(obj)) {
         rb_raise(rb_eTypeError, "can't clone %s", rb_obj_classname(obj));
     }
     clone = rb_obj_alloc(rb_obj_class(obj));
     RBASIC(clone)->klass = rb_singleton_class_clone(obj);
     RBASIC(clone)->flags = (RBASIC(obj)->flags | FL_TEST(clone, FL_TAINT))  
& ~(FL_FREEZE|FL_FINALIZE);
     init_copy(clone, obj);
     RBASIC(clone)->flags |= RBASIC(obj)->flags & FL_FREEZE;

     return clone;
}

VALUE
rb_obj_dup(obj)
     VALUE obj;
{
     VALUE dup;

     if (rb_special_const_p(obj)) {
         rb_raise(rb_eTypeError, "can't dup %s", rb_obj_classname(obj));
     }
     dup = rb_obj_alloc(rb_obj_class(obj));
     init_copy(dup, obj);

     return dup;
}


Dominik